1. Field of the Invention
This invention relates to tool feed devices for machine tools such as portable lathes.
2. Related Technology
Feed controls for incrementally advancing cutter tool bits into cylindrical metal work pieces while the tool bit traverses a section of the work piece, typically internal or external peripheral surfaces of the work piece, have various forms in the prior art. Such feed controls are utilized in connection with headstocks of lathes, milling machines and other machine tools to advance the cutting tool into the metal in small increments during machining procedures to remove metal from the work piece.
Typically, a feed screw is utilized to incrementally feed the tool bit into the work piece with the screw being caused to rotate by an actuator system that relies on rotation of the tool bit carrier about an axis of rotation during the cutting procedure. For example, in a portable lathe the tool bit holder is mounted on the headstock of the lathe which rotates relative to the lathe housing and carries the tool holder with the headstock while a feed screw is incrementally rotated periodically by means of an actuator system that utilizes a striker element on the fixed lathe housing that engages the feed screw actuator each rotation of the headstock.
Various adjustments are provided to control the degree of rotation of the feed screw to thereby control the amount of advancement of the tool bit into the work piece each rotation of the headstock. The cutter bit is advanced until the end of the cutting procedure and then the cutter bit must be returned to a starting location relative to the axis of rotation of the headstock.
Exemplary prior art patents illustrating portable lathes using cutting tool holders mounted on a rotatable headstock are U.S. Pat. No. 4,829,860 granted May 16, 1989 and U.S. Pat. No. 5,083,484, granted Jan. 28, 1992. In U.S. Pat. No. 4,829,860, a work piece is held concentrically within the headstock which rotates around the work piece and carries a tool bit holder on which a tool bit or cutter is mounted. The tool bit is advanced radially towards the axis of rotation during a cutting procedure while the headstock rotates about an axis of rotation.
U.S. Pat. No. 5,083,484 shows a different type of portable lathe that is supported by the work piece using a mandrel element extending through the central portion of the lathe tool. The headstock rotates concentrically with the mandrel and may carry a tool bit holder on its front face for machining the end of a pipe engaged by the mandrel.
It is typical to use self-contained tool feed modules mounted to the headstocks of such portable lathes as are described in the aforesaid patents, the tool feed module containing all of the elements required to support a tool bit and control its advancement into a work piece incrementally during machining procedures. Where a feed screw is utilized and is driven through a one-way clutch or other one-way drive device, returning a tool bit from an advanced position at the end of a cutting procedure back to a starting position is problematic because the feed screw is not readily rotatable in the reverse direction because of the presence of the one-way drive device and also because the feed screw is not necessarily accessible by a wrench or machine tool to reverse its rotation rapidly.